**7. References**

392 Biogas

Table 15 shows the minimum air addition for the individual processing grades of methane

**Weser Ems L Gas** 

**Air admixture** 

**in Vol.-%** 

**O2 in** 

94,000 92,429 5,506 1,700 0,645 10,226 12,999 0,619

96,000 91,778 3,442 4,600 1,208 10,154 12,996 0,611

98,000 91,163 1,488 7,500 1,741 10,086 12,993 0,603

99,500 90,702 0,091 9,700 2,126 10,035 12,988 0,597

For the high-caloric L gas mixtures (target properties according to Holland II L gas) the processed biogas is conditioned with air and LPG. Table 16 shows the correlating LPG-air

The gray-shaded areas show where a compliant combination of air and LPG additions is impossible. With increasing LPG additions, the necessary addition of air is limited by the maximum O2 volume fraction of 3 %. If too little LPG is added, only the lower calorific value range can be covered. The broadest coverage of the calorific value range lies in between and

**admixture**

**Calorific value** 

**Wobbe Index** 

**rel. Density** 

**HS,n = 9,653 - 10,047 kWh/m³** 

to achieve an L gas compliant Wobbe Index of under 13.0 kWh/m³ (NTP).

**Air admixtures to attain the target calorific value + / - 2%** 

Table 14. Air additions to the H gas properties under investigation

**Air to the Biogas** 

**in Vol.-% in Vol.-% in Vol.-% in Vol.-% in Vol.-% in kWh/m³ in kWh/m³** 

**Methane concentration after** 

 **Methane in** 

**admixture**

94,0 3,6 - 7,7 96,0 5,8 - 10,0 98,0 8,0 - 12,3 99,5 9,7 - 14,0

> **CO2 in**

**admixture**

Table 15. Minimum quantity of air to attain L gas specification

additions, to reach the calorific value range (+ / -2%).

is marked by the wider bandwidth of air additions.

**processing in vol -%** 

**Methane in Biogas** 

DIN 51 624 "Automotive Fuels - Natural Gas Requirements and Test Methods"


**1. Introduction** 

Chen et al. (1980) and Hashimoto et al. (1981).

The reactions involved in these steps are given below: • Phase-I. Solubilization of carbohydrate via hydrolysis

• Phase-II. Acidogenesis fermentation of glucose to acetate

the complex organic matter.

**19** 

Norazwina Zainol

*Malaysia* 

*Universiti Malaysia Pahang,*

**Kinetics of Biogas Production** 

Biogas produced in anaerobic digesters consists of methane (50%–80%), carbon dioxide (20%–50%), and trace levels of other gases such as hydrogen, carbon monoxide, nitrogen, oxygen, and hydrogen sulfide. Anaerobic digestion is a biological process in which organic material is decomposed by bacteria in the absence of air. The general technology of anaerobic digestion of complex organic matter is well known and has been applied for over 60 years as part of domestic sewage treatment to stabilize organic wastes. Bal & Dhagat (2001) points out that the anaerobic process is more advantageous than the aerobic process in organic waste treatment because of the high degree of waste stabilization, low production of excess biological sludge, low nutrient requirement and production of methane gas as a useful byproduct. Several studies have been carried out for evaluating kinetic parameters and model equations for anaerobic digestion by Siles et al. (2010), Borja et al. (2005), Jimenez et al. (2004), Raposo et al. (2009), Rincon et al. (2009) and Hu et al. (2002); these are all based on the Monod kinetic model (Monod 1950) and on the revised kinetic model developed by

In the microbiology of methanogenic process four different bacterial groups are identified as being responsible for carrying out the anaerobic digestion of complex organic matter. The first group of bacteria is hydrolytic bacteria which catabolizes carbohydrate, protein, lipid and other minor components of organic matter to fatty acids, H2 and CO2. The second group of bacteria is hydrogen producing acetogenic bacteria which catabolizes certain fatty acids and neutral end products to acetate, CO2 and H2. The third group of bacteria is homo acetogenic which synthesizes acetate using H2, CO2 and formate, and hydrolyzes multicarbon compound to acetic acid. Finally, the fourth group of bacteria i.e. methanogenic bacteria utilizes acetate, carbon dioxide and hydrogen to produce methane. The concerted action of these four bacterial groups ensures process stability during anaerobic digestion of

[C6H10O5]*n* + *n*H2O = *n*C6H12O6 (1)

**from Banana Stem Waste** 

Regulations on access to gas supply networks (Gas Network Access Ordinance - GasNZV) of 25 July 2005, last amended by Regulation amending the Gas Network Access Ordinance, the gas network tariff regulations, the incentive regulations and the electricity network tariff regulations of 8 April 2008.
